fast-xml-parser has an entity encoding bypass via regex injection in DOCTYPE entity names
28Vexday Risk Score
No sign of exploitation. No public exploitation artifact known so far.
ssvc Trackcvss 9.3epss 0.5%
exploitation probability
0.5%top 62% of all CVEs
observed exploitation
nono source reports it
fast-xml-parser allows users to validate XML, parse XML to JS object, or build XML from JS object without C/C++ based libraries and no callback. From 4.1.3to before 5.3.5, a dot (.) in a DOCTYPE entity name is treated as a regex wildcard during entity replacement, allowing an attacker to shadow built-in XML entities (<, >, &, ", ') with arbitrary values. This bypasses entity encoding and leads to XSS when parsed output is rendered. This vulnerability is fixed in 5.3.5.
CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:C/C:L/I:H/A:N
Affected products
NaturalIntelligence · fast-xml-parserReferences
https://access.redhat.com/errata/RHSA-2026:40984https://access.redhat.com/errata/RHSA-2026:41941https://access.redhat.com/errata/RHSA-2026:41944https://access.redhat.com/errata/RHSA-2026:51349https://access.redhat.com/errata/RHSA-2026:6174https://access.redhat.com/errata/RHSA-2026:6802https://access.redhat.com/errata/RHSA-2026:7110https://access.redhat.com/errata/RHSA-2026:7128https://access.redhat.com/security/cve/CVE-2026-25896https://bugzilla.redhat.com/show_bug.cgi?id=2441501https://github.com/NaturalIntelligence/fast-xml-parser/commit/943ef0eb1b2d3284e72dd74f44a042ee9f07026ehttps://github.com/NaturalIntelligence/fast-xml-parser/commit/ddcd0acf26ddd682cb0dc15a2bd6aa3b96bb1e69